Location of water-containing strata in well bores



Aug. 20, 1957 A A T. J. NOWAK 2,803,526

V LOCATION OF WATER-CONTAINING STRATA IN WELL. BORES Filed Dec. 3, 1954 @GSS REFRMCg- SEARCH United States Patent O LOCATION OF WATER-CONTAINING STRATA IN WELL BORES Theodore J. Nowak, Fullerton, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application December 3, 1954, Serial No. 472,991

17 Claims. (Cl. 23-230) This invention relates to an improved method for the determination of the location and vertical extent of permeable water-containing strata penetrated by a borehole, that is those from which water enters the bore in a producing well or into which water is injected from a water injection Well. It is particularly directed to an improved method for the determination of the location of such water injection or production strata in the secondary recovery of petroleum by water flooding.

Fluids are injected into permeable underground formations through a borehole penetrating such formations in several well-known types of operation. These operations include the underground storage of gases and secondary recovery operations in which gases or liquids such as water are employed to displace other valuable fluids through the permeable strata into a production Well. The thus displaced fluids are then recovered from the latter Well usually by conventional pumping techniques. The secondary recovery operations are ordinarily resorted to only when the primary recovery processes, such as flowing and pumping, have become uneconomical.

In the secondary recovery processes, several Wells are drilled into and through the permeable subsurface strata containing valuable fluids. These wells are ordinarily spaced in a horizontal plane in a regular geometric pattern. For example, an injection well may be surrounded by 3, 4, or 6 production wells spaced at the corners of a triangle, square, or hexagon, respectively. An injection fluid, such as gas or water or other specialized fluid, is injected into the injection well, passes into and through the various permeable strata penetrated thereby, and drives the valuable fluids present in such strata toward the surrounding production wells. Often the geologic structure of the fluidcontaining formation is such that a plurality of permeable strata exists. Each stratum of the plurality may vary in thickness as well as in fluid permeability and thus the injection fluid will pass at different rates into the different strata.

It is highly important to the proper operation of these secondary recovery processes to be able to ascertain eX- actly the location of each permeable stratum accepting fluid from the well bore as well as the rates at which fluid enters the various strata.

In oil production operations it is desirable to locate and determine the location and thicknesses of water-producing strata in an oil producing interval in order to plug off the water strata and thus cut the operating costs. In secondary recovery of oil by water flooding, the injectivity profile is needed to obtain diagnostic evaluation of water intake distribution over the injection interval. If the distribution is unfavorable among the strata, corrective measures can be taken to provide better control.

Conventional spinner logs and the like are often used to locate points of ingress or egress of uids in well production and secondary recovery processes. These logs are subject to a number of serious problems. Nearly all well bores are provided with casings to support the walls of the ICC borehole. These casings are perforated along the casing length, supposedly opposite a permeable stratum into or from which fluid flow is desired. Leaks in the casing at points other than the perforated sections appear in the spinner log as a flow point. Any vertical flow of fluid between the casing and the borehole wall, which may either occur after passage of the fluid through the perforations and before entry into a permeable stratum or after discharge from the stratum and before passage through the perforations, renders a spinner log inaccurate as regards the true position at which the fluid enters or leaves the permeable formation. The spinner log is not subject to this disadvantage in an uncased well bore. However, it is a serious disadvantage in the usual cased boreholes.

To identify the water-producing strata in an oil well and to obtain the injectivity profile in a water input well the following method is proposed: (l) a temperature log is run in the well bore under normal operating conditions, (2) a chemical which generates heat when contacted with water is injected through the bore into the strata, and (3) subsequently a second temperature log is run in the Well to locate temperature anomalies.

The present invention is directed to an improved method of logging a borehole into the earths crust and through which fluids are passed for production from or injection into one or more permeable subsurface strata. The method permits the determination of the absolute location or depth and the absolute thickness of the permeable strata receiving fluid from or delivering fluid to the bore, and in addition permits a determination of the absolute rate of fluid flow into or from each such stratum. The subsequent description will be conducted in two parts, one relative to the logging of an injection well through which water is passed into a permeable petroleum-containing formation to effect the secondary recovery of the crude petroleum, and the other part relative to the logging of a production well from which crude and water are obtained. It should be understood, however, that the method may likewise be employed for the determination of injection profiles of gas entering underground reservoirs, secondary recovery processes using gas drive, in processes involving the injection of any other fluids into underground strata, or in operation of gas producing wells, etc.

Two highly important features of the present invention include the ability of the method to perform with high accuracy in uncased as well as in perforated cased boreholes. Another important feature is that the method permits the distinguishing of the rate of fluid injection into or delivery from adjacent permeable strata which have differing fluid permeabilities; that is, strata not separated by impermeable strata.

It is a primary object of this invention to provide an improved method for logging boreholes.

A more specific object of this invention is to determine the fluid flow profile in a well bore through which fluids are passed for injection into or after fluid delivery from permeable underground strata penetrated by the bore.

A more specific object is to provide a method for the high accurate determination of the absolute length of a section of a well bore throughout which fluid passes from the bore into underground permeable strata as well as a highly accurate determination of the relative rates at which such fluids enter these permeable strata.

One specific application of the present invention is in the determination of the location of water entry into subsurface petroleum-containing strata and the relative distribution of the injected water into a plurality of permeable strata.

It is another specific object to provide a highly accurate method for quickly determining the location of water entry into or from the underground in a well bore by running a temperature log of the fluid in the bore during water injection or production and again during shut-in conditions immediately after the injection of a water reactive heat generating substance into the various permeable strata containing water and penetrated by the borehole.

Other objects and advantages of this invention will become apparent to those skilled in the art as the description thereof proceeds.

Briefly, the method of the present invention involves the accurate temperature logging of the well bore under various operating conditions, the introduction of an exothermally water reactive material into the permeable strata, and a comparison of the temperature logs so obtained to determine the limits of the various permeable strata in fluid ow communication with the well bore as well as the relative lluid ow rates into or from each stratum.

The method is based on: (l) the generation of heat wherever a chemical reagent contacts water in the strata, (2) the low thermal conductivity of the strata which results in connement of the heat within the strata over long periods, and (3) the measurement of the temperature disturbances or anomalies associated with the differential heating in the strata. Because interstitial water is present in all sedimentary strata, heat will be generated in all of them; however, the magnitude of the heat produced, and hence the increase in temperature, will depend upon the porosities, permeabilities, and the water saturations in the strata. Strata producing or taking water will be associated with relatively greater temperature increases than those containing interstitial water only. The resulting temperature disturbances can be measured in the well bore by a continuous surface recording instrument located at the surface, or by making appropriate station stops with a subsurface recording mstrument.

In the present invention, accurate measurements of the temperatures of the fluid at various depths within the well bore are performed during the normal fluid flow in that borehole to determine a normal operating temperature gradient, e. g., an injection or a production temperature gradient as the case may be. Then an isolated mass or body of material which is exothermally reactive with water, is introduced into and is pumped down the bore. This material is isolated from the fluid in the well bore by a pair of rubber cups, or by adjacent layers of inert anhydrous uids of approximately the same density so as to prevent premature mixing and reaction. The pumping is continued at a relatively low rate so that the iluid moves through the borehole in streamline flow, without appreciable turbulence, and substantially no mixing.

When the reactive fluid reaches the permeable strata, it ows radially outward from the bore as a toroidal shaped mass of constant volume through each of the permeable strata. Because of the relatively small equivalent diameters of the serially connected interstices in the permeable strata the lineal velocity is greatly increased and the llow becomes turbulent. Thorough mixing of the reactive injected fluid and fluids present in the interstices takes place, and heat is generated therein to an extent determined by the amount of water present in each permeable stratum.

The liberated heat raises the temperature of the liuid and the permeable rock to values above those which are characteristic of a well bore during normal ow as described fully below. Accordingly, a second temperature log is run immediately after the entry of the reactive fluid into the permeable strata and indicates by the detection of the high temperature anomalies the exact location and vertical extent of such permeable strata even though covered by a casing, and permits quite an accurate evaluation of the permeability of such strata from the measured temperature rise.

The foregoing steps may be applied either to an injection well or to a production well and in either case the temperature anomalies indicate the location and extent of permeable strata. With an injection well the measured temperatures are usually below the geothermal gradient, and with a production well they are above it.

The geothermal temperature gradient is dened as the normal variation in temperature of the undisturbed subsurface strata with distance below the earths surface. Ordinarily the temperature of the subsurface rises roughly 20 F. per thousand feet of depth along this geothermal gradient. There are several ways in which the geothermal gradient may be established. In an oil eld in which a great number of wells have previously been drilled, a correlation of the bottom hole temperatures with depth of as many such wells as possible may be made. A measurement of the bottom hole temperature just following completion of the well is the most desirable since thermal disturbances at this point are then at a minimum. The geothermal gradient may also be determined by running a highly accurate temperature log through the bore after the bore has come into thermal equilibrium with the subsurface; that is, after a relatively long period of non-use during which no fluid tlow through the bore has been elected.

The normal temperature of subsurface strata progressively increases with depth, often rising to 250-300 F. at 10,000 foot depths and to higher Values at greater depths. These temperatures are generally in excess of the temperatures at which the injection lluid is introduced into the injection well. Consequently, as the injection proceeds and the lluid flows downwardly through the well bore toward the permeable strata, the surrounding strata are cooled to temperatures below the normal geothermal temperatures. When injection is stopped and the well is shut in, the cooled portions of the strata adjacent the well bore and the stationary uid therein are reheated by heat Howing radially inward by conduction from the uncooled outer reaches of the surrounding formations toward the bore axis. The temperatures will eventually reassume the normal geothermal temperature gradient if the well is shut in over a prolonged period.

It is possible to analyze the rate of return to geothermal temperatures during the shut-in period by running temperature logs of the bore while no uid flows. This procedute is very accurate but is somewhat time consuming because the time required to elapse between the running of the injection log and the shut-in log may be as great as 6-8 days. The present procedure described below in respect to injection well logging avoids this problem, and requires no appreciable time loss due to extended shut-in. The temperature log may be run in 10-15 minutes shut-in time following entry of the reactive uid in the permeable strata, and then full rate injection is continued.

The first step in the method of this invention as applied to injection well logging is the determination of the injection temperature gradient through the borehole or at least through that part of the borehole embracing the strata receiving lluid therefrom. This temperature log indicates the changes in temperature of the injection lluid as it traverses the borehole. In most cases the lluid, when introduced, is at a higher temperature than the temperature of the formation through the rst few hundred feet of depth of the well and in this region the injection fluid loses heat into the formation and is cooled. However, with increasing depth the normal or geothermal temperature of the subsurface rises and heat is received by the injected uid and it rises in temperature. This heat is conducted radially inward toward the borehole axis.

When a permeable stratum deep in the subsurface is encountered, this usual radial inward flow of heat by conduction is halted or neutralized by the radial outward flow of injected lluid into the permeable stratum. Thus that part of the injection uid passing through the borehole remains unheated as indicated by a constant temperature between the top and the bottom of the permeable stratum. From this constant temperature noted in the log, which is run to determine the injection gradient, the upper and lower limits h1 and h2 of a permeable stratum receiving iluid from the well bore may be accurately located. This is true even though the uid entering such permeable strata leaves the casing at a point above or below the particular stratum and enters the stratum after flowing vertically for some distance between the casing and the borehole wall. In such a case, the constant temperature portion of the injection gradient appears opposite the permeable strata receiving the iluid even though that portion of the casing is not perforated. Such injection gradients are shown as curves in Figure 2 subsequently described.

The second step involves the introduction of a water reactive heat liberating substance via the well bore into the subsurface permeable strata wherein the iluid is mixed and reacts with water present to liberate heat, the temperature effects being detected and recorded during the performance of the third step of the invention.

For the above method, several types of chemicals, capable of exothermic reaction on contact with water, can be injected into the strata. Examples of suitable chemicals are: an alcohol solution of an alkali metal such Ias a solution of isopropanol and sodium, a dispersion of sodium or other alkali metal in an inert solvent such as a dispersion of 5-50 micron size sodium particles in kerosene which is presently commercially available, a liquid alloy of sodium or potassium, and la solution of anhydrous acids in inert solvents such as hydrochloric acid-carbon tetrachloride, sulfur dioxide-oil, chloric acidalcohol, or chloro-sulfonic acid alone, etc. For the practice of this method, isopropanol-sodium solution is desirable because large quantities of heat are liberated on contact with brine, it is relatively easy to prepare, and it is inexpensive.

The ow rate of the injection iluid containing the isolated pill of water reactive material is maintained at a value so that the llow of the water reactive material down through the well bore is in the streamline region and no substantial turbulence and iluid mixing occurs. This is achieved by considering the diameter D in feet of the path through which the iluid flows, e. g. that of the bore or casing, the iluid density p in pounds per cubic foot, the viscosity p. in pounds per foot seconds, and controlling the iluid ow rate through the well bore at a velocity V in feet per second so that the Reynolds number within the borehole is less than 2100, and preferably below about 1000. [The leynolds number is defined as follows:

Reynolds numberwherein the factors on the right-hand side of the equation have the units as designated above. Preferably the injection water rate is gradually decreased to a rate at which such streamline flow of the reactive material will occur. The injection water llow at the well top is then substituted with the reactive iluid llow of the same rate, then followed with more water at the same rate. Under such controlled conditions substantially no mixing or exothermic reaction between the reactive material and the injection fluid, if water, occurs.

When the pill is isolated mechanically from the injection iluid, such as between a pair of mechanical plugs such as rubber cups or packer type straddle tools, higher velocities through the well bore to the permeable strata can be maintained, without turbulent mixing, but the cups must usually be retrieved.

The injection of the iluid is continued until the reactive iluid enters the permeable strata penetrated by the well bore. This is determined by pumping into the bore, after addition of the reactive fluid at the surface to the injection iluid, a volume of injection iluid slightly in excess of the volume of the borehole and controlling its rate so that the reactive iluid llows in streamline flow. This causes the pill of reactive iluid to enter the permeable strata, and the reactive iluid commingles with the injection iluid in the interstices of the strata causing the exothermic reaction with the water therein and liberation of heat. In liquid flows through porous rock, practically in all cases turbulent ilow is encountered and excellent turbulent mixing is obtained.

The third and final step involves briefly shutting in the well by termination of the injection fluid flow and running a shut-in temperature log in the borehole at least over the suspected area of iluid entry into the penetrated strata. The heat liberated in such strata causes a significant local temperature rise in the then stationary fluid in the bore opposite each of the strata into which the injection iluid has carried the reactive fluid. These temperature anomalies indicate the location of water strata.

Following the above described three essential steps of this invention, the injection fluid llow is readjusted to the normal rate and conventional secondary recovery operations are continued.

The data obtained in this injection well logging process include two temperature logs, one taken during normal injection of the injection iluid, and the other taken immediately after the entry and mixing of the reactive fluid in the permeable strata during a brief shut-in period.

From an inspection of the injection temperature log, the vertical extent and depth limits of each permeable stratum receiving injection iluid are fixed by constant temperature or zero temperature gradients as above described. From an inspection of the shut-in temperature log, regions of abnormally high temperature are found between these same depth limits due to heat liberated at the faces of and within the permeable strata. An analysis of these tem`- perature anomalies as described below permits an accurate evaluation of the permeability, porosity, water content, etc. of each penetrated stratum.

Certain boundary heating effects are noted in the shutin gradient at points corresponding to the upper and lower limits of the permeable strata. These boundary effects are caused by vertical heat llow from the warmer impermeable strata above and below a given permeable stratum into which the injection iluid passes. These boundary effects prevent the formation of sharp temperature changes in the shut-in gradient opposite the upper and lower limits of the permeable strata and hence, with one presently discovered exception, the limits of the permeable strata are best determined from the injection gradient where sharp indications of constant injection iluid ternperature appear.

The one exception referred to above is found in those cases in which two permeable strata are encountered sideby-side unseparated by a layer of impermeable rock, the two permeable strata having different iluid permeabilities. Under such conditions, the shut-in gradient shows a relatively sharp temperature anomaly opposite the point on the borehole axis at which the permeable strata of different permeability are in Contact.

After following the above described steps in obtaining the injection gradient and one or more shut-in gradients by temperature logging the well bore, the exact upper and lower limits of the permeable strata receiving iluid from an injection well bore may be located. In addition, the points at which two immediately adjacent permeable strata of differing iluid permeabilities are in contact may also be determined. The foregoing determinations have been proven accurate whether the borehole is uncased through the permeable interval or is provided with a perforated casing through this interval or is partly cased and partly uncased. These logging steps permit what might be called a qualitative determination of the presence of permeable iluid-receiving strata; that is, the location of the upper and lower limits of such strata. The addi- 7 tional steps by which a quantitative determination of injection rates are described below.

The geothermal temperature gradient is a smooth curve, the temperatures rising uniformly with depth from the surface. The injection temperature gradient is also a farily smooth curve, with the constant temperature portions opposite permeable strata receiving nid as discussed above. The shut-in temperature gradient is also a smooth curve except opposite the permeable strata, the shut-in temperatures Ts at any given depth rising regularly with time from the injection temperature value Ti to the normal geothermal value Tg. The regular portions of a given shut-in gradient are smooth, but opposite the permeable strata anomalously high temperatures are noted due to the heating effect of the exothermic reaction therein. A simple extrapolation of the regular portions of the shutin gradient opposite the impermeable strata across the temperature anomalies opposite strata receiving lluid gives the extrapolated equivalent shut-in temperatures Tes which would be expected from the shut-in gradient opposite the permeable fluid-receiving strata had no exotherrnic reaction taken place. At a given depth in a permeable stratum, the shut-in temperature anomaly AT is Ts-Tes and is due solely to the heating effect on the permeable stratum due to exothermic reaction of Huid injected thereinto from the bore. lt is proportional to the rate of water injection through the differential stratum thickness dh at the given depth. The integral of AT as a function of depth h of the permeable strata is proportional to the volumertic rate of water injected into the whole stratum prior to shut-in. These temperature gradients and the anomalies referred to are more clearly shown in Figure 2 described below.

The mathematical relationships which are employed in the determination of the water injection proles from the shut-in temperature anomalies AT and the permeable strata depth limits h1 and h2 are simple.

At a given depth h in the permeable strata and after the exothermic reaction, the temperature anomaly AT is equal to:

Mfrs-Tes (1) or the difference between the shut-in temperature TS and the extrapolated normal shut-in temperature Tes. The change of the value of AT with depth h through the permeable stratum is readily determined from the log of the actual and the extrapolated shut-in gradients referred to above, thus AT is a known function of depth h.

The shut-in time in the present invention is so short that the approach from actual normal temperature toward geothermal temperature is intinitesimal and Tes can usually be substituted with the normal injection temperature Ti from the injection gradient.

As indicated above7 it has been found that the integral of AT as a function of the depth of the permeable stratum h is proportional to the volumetric tlow rate of injection water into the stratum. The integrated product A is:

h2 A=jlL1 Arufjhjfm (2) and the individual water injection rate Q is:

Q=kA (3) The sum of the volumetic injection rates Q into each EA:A1+A2+A3 An s permeable stratum equals the uid injection rate Q0 at the well bore inlet, or:

Qo=Q1lQ2lQ3 Q1 (5) Substituting Equations 3 and 4 in Equation 5, the total water injection rate Qn is:

The individual volumetic water injection rates are then directly calculable from Equations 3 and 6 and are equal to:

A @Fal-l 7) An call] (s) ete.

The drawings, discussed below, clearly lllustrate the various temperature gradients discussed above and indicate the anomalous temperature dilerences AT between the extrapolated or expected shut-in temperature Tes and the actual logged shut-in temperature Ts opposite the permeable strata receiving uid.

The total water injection rate Qn multiplied by the ratio of the integrated product for a given stratum to the total integrated products for all strata is equal to the individual injection rate as indicated in Equations 7 and 8.

The temperature logs are ordinarily plotted as depth in feet as ordinate against temperature as the abscissa and the integrated temperature difference with respect to stratum thickness through each permeable stratum is readily determined by graphical integration of such logs; that is, it is equal to the anomalous area between portions of the equivalent (or injection) and actual shut-in gradients which lie between the depth limits corresponding to the upper and lower depths of the particular stratum. These temperature gradients are conveniently recorded automatically on a temperature recorder of the moving chart type, which is well-known and commercially available, wherein the chart moves in position corresponding to the depth in the well bore of the temperature sensitive device employed to measure the fluid temperatures therein.

The process of the present invention can also be applied in the logging of production wells to determine the location and vertical extent of permeable strata penetrated by the well bore and which contain water and produce it at various rates into the bore. Production of undesired brine simultaneously with crude petroleum is an expensive and useless waste of energy, and the accurate location of such brine producing strata permit remedial plugging measures too be taken whereby the water cut of the produced pertoleum may be reduced or even eliminated.

The procedure in treating an oil producing well with the chemical involves injecting the chemical as a pill sandwiched between two inert fluids such as oil so that no water contacts the chemical pill in the well bore. The pill is of suicient volume so that in the water strata it will displace any of the inert uid that previously entered the strata ahead of the pill to a radial distance where the doughnut shaped ring of inert Huid is broken or reduced in radial thickness to an extent where the water commingles with the chemical.

The rst step in this modication of the process is the determination of a production gradient, which is a log of the variation in temperature Tp of produced fluid with depth throughout the well bore, or at least over the suspected production interval, while the well is being produced at the normal rate. This production gradient is determined by running a temperature sensitive device through the bore and recording the indicated temperature as a function of depth much the same as was done in determining the injection gradient described above. The production gradient usually involves temperatures slightly higher than those in the geothermal gradient for the same depth because the uids produced at the greater depths are warmer than the upper rock and they remaln warmer during fl'ow to the surface than the surrounding rock at higher levels.

The second step in this modification of the invention involves the termination of production, the introduction into the well of an isolated pill or mass of material which is exothermally reactive with water, and then pumping this pill with the fluid ahead of it down the well bore into the various permeable strata. Again the pumping rate is controlled to maintain streamline ow in the bore so as to avoid premature mixing with water unless a mechanical means is used to isolate the chemical from the fluid present in the well bore. Suicient uid is injected to cause entry of the reactive material into admixture with water in the permeable strata as described above. Heat is therein liberated as in injection well treatment raising the temperature of fluid at the face and within the permeable strata.

The third step is to shut in the well for a short period and run a second temperature log to Adetermine the shut-in temperatures T' and the location and magnitude of the production gradient anomalies resulting from the exothermic reaction of the injected reactive material with water present in the various permeable strata. These anomalies determine the location of those permeable strata containing water and the magnitude of the heat effect is a measure of the quantity of water present in a given permeable stratum of known vertical extent.

The well is then treated if found necessary and desirable to seal oif the discovered water producing stratum or strata and then is placed back on production.

Thus it is seen that the same principles of this invention can be applied to the location of permeable strata penetrated by a well bore and either producing or receiving water to or from the bore, and the steps are substantially identical.

The method of the present invention as outlined above,

the nature of the data obtained, and the nature of the various temperature gradients referred to above are shown more clearly in the accompanying drawings in which:

Figure 1 is a schematic view in cross section of an injection well showing a temperature logging device used in the method of temperature logging, and

Figure 2 indicates the appearance of the geothermal, injection, and shut-in gradients obtained in the method of this invention.

Referring now more particularly to Figure l, well bore provided with casing 12 extends from the earths surface 14 down to and through two permeable strata 16 and 18 separated by strata 17, 19,`and 20. For purposes of describing the procedure of this invention to logging of injection wells, these strata are impermeable to Huid flow, but in the subsequent description of production well logging strata 17 and 19 only are impermeable, strata 16 and 18 produce water and stratum 20 produces oil and gas. The portions of casing extending through the permeable strata are provided with perforations 22 which permit the ow of injection fluid into or production fluid from the permeable strata. Line 24 controlled by valve 26 is provided to control the flow rate of fluids into or from the permeable strata penetrated by the borehole.

A temperature sensitive device indicated generally at 28 is suspended within well bore 10 by cable 30 which passes upwardly through the top of the well bore sheave 32 and onto cable drum 34. Through slip rings, not shown, temperature recorder instrument 36 is connected to cable 30, and connection 37 permits instrument 36 to record the depth of element 28 in the bore. A temperature log is obtained by passing temperature sensitive means 28 through the well bore in contact with the fluid present within the bore and the temperature indications obtained are plotted as a function of position or depth within the well bore by instrument 36. The temperature sensitive means may be moved slowly through the well bore and continuous recordings made, or it may be halted every few inches or every few feet while the temperature reading is obtained and recorded. The latter method is preferable since a more highly accurate temperature reading is thereby obtained.

Referring now more particularly to Figure 2 several curves are shown indicating typical temperature gradients and temperature anomalies obtained in the practice of the process of this invention. Figure 2 plots measured temperatures of the fluid in well bore 10 as a function of depth in the borehole from the surface, and gradients are shown typical of those obtained in the practice of this invention as applied to the logging of injection wells as well as production wells.

In either the injection or production of fluids in well bore 10, the geothermal gradient 40 is shown in Figure 2 indicating the normal temperature variation with depth ot fhe undisturbed underground formations. During secondary recovery operations the injection water usually has a temperature lower than the geothermal temperature and this causes the injection gradients as determined by a logging operation after long continued injection to include temperatures considerably below the normal geothermal temperatures as indicated by curve 40. The injection gradient is indicated in Figure 2 by curve 42 which is the solid line to the left of geothermal gradient 40 and denoted Ti. ln a flowing production well however the fluids produced from a given strata are substantially the same temperature as the geothermal value, ignoring for the moment localized temperature decreases due to the escape of gas in the well bore from the face of the permeable strata. The production gradient therefore includes temperatures Tp which are slightly higher than the geothermal gradient because of the upward flow of the warm fluids from lower points in the well bore through the superimposed cooler strata. This is indicated by production gradient 50 in Figure 2 which is the solid line just to the right of geothermal gradient 40.

For the first part of the description it will be assumed that strata 17, 19, and 20 are impermeable and that injection water is being injected into permeable strata 16 and 18 in a secondary recovery operation. In the second part of the description it is assumed that strata 17 and 19 only are impermeable, permeable strata 16 and 18 are producing crude petroleum and water into well bore 10, and stratum 20 is producing crude without water under sufficient pressure to ow to the surface.

To determine the location of permeable strata 16 and 18 in an injection well and to ascertain the relative rates at which the injection fluid is entering the permeable strata according to this invention, the following steps are carried out. While the injection uid is continuing at the normal rate of 1000 barrels per day, a temperature log is run from the bottom of the hole at least over the interval embracing strata 16 and 18 to obtain the injection temperature T1 and determine the injection gradient ind-icated by curve 42 in Figure 2. From an inspection of this curve it is seen that the water injected at the surface is higher in temperature than the normal surface rock temperature and accordingly is first cooled and then warmed again slightly as it passes down through the borehole because the surrounding rock at lower points in the bore has a geothermal temperature greater than that of the water. The Water in the bore opposite the permeable strata 16 and 18 remains at a substantially constant temperature because the normal geothermal heating effect is neutralized by the outward radial flow of injection water which absorbs and carries any geothermal heat outwardly away from the bore. This is illustrated in Figure 2 by the two isothermal portions of curve 42 indicated as 44 and 48. A portion of the injection water enters stratum 16 and the rest continues downwardly from opposite stratum 16, passes through impermeable strata 17, 19, and 20, and enters stratum 18. Because no radial outward flow of injection water occurs opposite these yimpermeable strata, the normal geothermal heating effect continues causing the temperature of the injection uid to rise slightly in this interval and the increasing temperature is indicated in curve 42 as portion 46. The temperature of the water between the bottom of lower permeable stratum 18 and the bottom of the bore rises rapidly to the geothermal temperature as indicated by the lowermost portion of curve 42 which is herein indicated as 52. This is due to the fact that there is no net uid ow in the bottom of the bore and the normal geothermal heating phenomenon raises the temperature of the undistributed fluids therein to values substantially identical with those on the geothermal temperature curve 40.

A pill of reactive material which reacts exothermally with water, and which in this example consists of 300 gallons of a commercially available mixture prepared by dispersing 50 pounds of sodium as 20 micron particles in 300 gallons of kerosene, is added to the injection water and isolated therefrom by gallon plugs of pure kerosene above and below the pill. This material was injected at a rate of 100 barrels per `day over a period of about 1.9 hours. The water injection was continued at a rate of 100 barrels per day for an additional 5.7 hours which was sufficient to inject the pill of reactive fluid into the permeable strata. The 100 barrel per day flow rate was suicient to keep the kerosene pill flowing in streamline flow in the injection conduit which had a diameter of 2.5 inches. This injection well was 3900 feet deep, the total injection time was about 7.6 hours.

With the kerosene-sodium dispersion in the permeable strata, the water injection was then terminated for a period of about 30 minutes during which time a temperature sensitive ldevice was run to the bottom of the well to measure the shut-in temperature Ts and thus determine a shut-in gradient to determine the location and magnitude of the injection temperature anomalies caused therein by the heat liberated from the reaction of the sodium particles with the water present within permeable strata 16 and 18. The result is shown in Figure 2 wherein shut in injection gradient 54 exhibits injection temperature anomalies 56 and 58 at depths equivalent to those of strata 16 and 18. As indicated above, the area between the injection gradient and the shut-in gradient at these anomalies 56 and 58 is proportional to the entire water injection rate of 1000 barrels per day. The total rate of water injection Qn multiplied by the ratio of anomalous area 56 to the total anomalous area 56 plus 58 is equal to the injection rate Q1 into permeable stratum 16. By an analogous calculation an injection rate into any other stratum may be determined, and when there are only two permeable strata the injection rate into the other is obtainable by dierence.

Following this determination, which consists in running a shut-in temperature gradient, the injection water may be continued at the former rate. There is substantially no time lost in secondary recovery operations to make the determinations described above because the shut-in time need only be long enough to permit running of the shut-in temperature over the suspected injection interval. In the above case this required only 30 minutes and it was found that the shut-in temperatures TS opposite the impermeable strata were substantially identical to the previously determined injection temperatures T1 at the same points.

In applying the process of the present invention to determine the location of waterproducing strata penetrated by the borehole the procedure is practically the same, but the temperatures encountered are generally higher than the geothermal temperatures rather than lower as in the case of an injection well. For purposes of the following description, strata 17 and 19 are impermeable, stratum 20 produces crude with no water, and strata 16 and 18 produce water and some oil and gas. In Figure 2 the geothermal gradient is indicated by curve 40 showing a gradually increasing subsurface rock temperature with depth. The first step is the determination of a production gradient by continuing the oil flow at the normal 600 gross barrels per day rate and running the temperature sensitive device through the well as above described to determine temperatures Tp in the production gradient. During production, uids flow from permeable strata 16, 18, and 20 substantially at the temperature of those strata and flow upwardly through cooler regions within which they lose heat and gradually decrease in temperature as they progress to the surface as indicated by production temperature gradient 50.

ln the second step the production is discontinued, an exothermally reactive pill of material is introduced into the borehole and isolated from the fluids therein by physical means. In this case the reactive material was 20 barrels of a dispersion containing 20% by weight of sodium of particle size range up to l0 microns dispersed in absorption oil. Crude oil was pumped back into the well at a rate of 100 barrels per day for three hours in streamline ilow so as to bring the reactive material to the productive level and cause its injection into the various permeable strata wherein it is mixed and reacts with the water present therein and liberates heat in an amount proportional to the water present, and this in turn is proportional to the water production rate.

In the third step the injection was discontinued for a period of minutes during which time the shut-in production gradient shown in Figure 2 was run. It is substantially the same as production gradient S0, that is, values of Ts' are about the same as values of Tp adjacent the impermeable strata, except that it includes the dotted portion of the curve to the right of production anomalies 60 and 62. Herein the temperatures TS' were found to rise sharply throughout intervals 64 and 66 opposite the water producing permeable strata 16 and 18 due to the liberated heat from the reaction of water present in these strata with injected dispersion of the sodium particles that migrated into the interstices of the strata and wherein the particles are trapped by deposition by liltration in the immediate vicinity of the borehole. No temperature anomaly appeared opposite oil producing stratum 20 because substantially no water was produced therefrom.

Except in the case where a penetrated stratum is producing almost entirely water into the well bore, the production temperature anomalies 60 and 62 are generally smaller in area and accordingly involve lower temperature differences than those previously described in connection with water injection. The amount of water present in each production stratum is estimated by the same method as given above except that the integral A for each anomaly is determined from T s-T p, the total integral 2A is related to the total water production, Qn', and incremental water production Q', is equal to This method can also be applied to clean oil producing wells (e. g. no Water cut) to determine the amount of interstitial water present in the strata and how the interstitial water varies in amount among the strata.

A further modification of the present invention exists in the addition of an optional step of placing either an injection well or a production well on production for a short period after introducing the exothermally reactive pill into the strata in order to allow further commingling of water present in the strata with the injected chemical to complete the exotherrnic reaction. The well may be alternately injected and produced for several cycles if desired. This procedure is often very helpful in the logging and analysis of the strata containing relatively small amounts of interstitial Water.

Although the description in Figure 2 by way of two examples involved two diierent concentrations of a chemically reactive material and two dilerent means of physically isolating the material in transit through the borehole, other materials and methods may be used. Other permissible water reactive materials include: sodium-potassium liquid solution, chlorosulfonic acid in isopropanol, hydrochloric acid gas dissolved in dimethyl formate, etc.

Other suitable examples for physically isolating these reactive materials from water within the well bore in addition to those described above include a straddle tool packer, or rubber cups preceding and following the pill with suitable check valve arrangement at bottom of tubing, and the like.

A particular embodiment of the present invention has been hereinabove described in considerable detail by way of illustration. It should be understood that various other modifications and adaptations thereof may be made by those skilled in this particular art without departing from the spirit and scope of this invention as set forth in the appended claims.

I claim:

l. A method for logging well bores to determine the location of water-containing permeable strata penetrated by said well bore which comprises measuring the variation in temperature of the tluid within the well bore at least throughout the permeable strata interval while continuing normal iluid ow between said well bore and said strata, then terminating said normal uid ow, then injecting into each of said permeable strata a uid out of contact with well bore fluids and containing an agent exothermally reactive with water whereby said agent mixes and reacts in said permeable strata with said water and liberates heat therein, and remeasuring the variation in temperature of the uid within said well bore opposite said permeable strata thereby detecting the presence of water-containing strata from temperature anomalies consisting of regions of abnormally high temperature opposite said permeable strata.

2. A method according to claim 1 in combination with the step of physically isolating the water reactive fluid from the fluids passing through said borehole into said permeable strata to avoid premature mixture and reaction with any water present in the bore.

3. A method according to claim 2 wherein the physical isolation of said reactive tluid is accomplished by pumping a volume of inert anhydrous iluid into the well bore ahead of said water reactive uid, pumping another volume of inert anhydrous fluid into said well bore immediately after said reactive fluid, and controlling the ow rate within said bore to maintain said reactive uid moving through said bore between the volumes of inert uid in streamline ow conditions whereby no substantial intermixing of said fluids occurs until said water reactive tluid reaches and enters said permeable strata.

4. A method according to claim 2 wherein the physical isolation of said water reactive fluid is accomplished by the steps of placing a mechanical plug in the bore, pumping said water reactive iluid into said well bore, and then placing another mechanical plug in said bore after said liuid.

5. A method for the location of subsurface water containing permeable strata penetrated by a well bore which comprises passing a temperature sensitive device through said well bore, measuring the temperature of the liuid flowing therethrough at various measured depths in said well bore While continuing the uid iiow therethrough at the normal operating rate to determine an operating temperature gradient, introducing into said well bore a volume of iluid containing an ingredient exothermally reactive with water, injecting additional fluid into said borehole to move said volume of fluid therethrough and into admixture with fluids present in said permeable strata wherein reaction with water and heat liberation occur, controlling the uid velocity of fluids ilowing through said borehole to maintain said volume of fluid in streamline iiow therein to avoid premature reaction, terminating the injection of fluid into said well bore, again passing a temperature sensitive device through said well bore, measuring the temperature of the fluids opposite at least the permeable strata at various measured depths in said well `bore in the substantial absence of iluid flow to determine a shut-in temperature gradient characterized by regions of abnormally high temperature at depths opposite permeable water containing strata, and then continuing the normal flow of uids through said borehole.

6. A method according to claim 5 wherein the fluid containing the exothermally water reactive ingredient is selected from the group of exothermally water reactant materials consisting of alkali metals dispersed in inert solvents, solutions of anhydrous acids in inert solvents, liquid alkali metal alloys, alkali metal alcoholates, and chlorsulfonic acid.

7. A method for determining the location of permeable strata penetrated by a borehole and in which an injection fluid is pumped through said bore hole and into said strata, which method comprises measuring the variation in temperature of the injection fluid with position within said borehole at least through the interval penetrating said permeable strata while continuing the normal injection fluid llow rate, then terminating the introduction of injection fluid at the top of said borehole, then injecting into the permeable injection strata a uid out of contact with borehole fluids and containing an agent exothermally reactive with said injection lluid whereby said agent mixes and reacts with said uid within said permeable strata and liberates heat therein, and remeasuring the variation in temperature of the fluid with depth within said borehole opposite said permeable injection strata thereby detecting the depth and extent of said injection strata from detected high temperature anomalies.

8. A method for determining the depth and extent of permeable injection strata penetrated by an injection well in a water ooding operation to recover hydrocarbons which comprises measuring the variation in temperature T1 of the injection water with depth h in said well at least throughout the interval embracing the permeable strata while continuing the normal flow rate of injection water, then terminating said injection water ow, immediately following it with a stream of a volume of reactive uid containing an agent exothermally reactive with water pumped into said injection well and physically isolated from the injection water therein, controlling the tlow rate of said reactive fluid so as to maintain it in nonturbulent streamline flow through said well, then pumping further injection water into said well after and isolated from said reactive fluid while maintaining streamline ow conditions for a suicient time to inject the physically isolated reactive uid into said permeable strata wherein it mixes in turbulent flow and reacts with injection water therein to liberate heat, then terminating the injection water ilow in said Well, and again measuring the variation in temperature Ts of the injection water with depth h at least throughout the permeable interval in the absence of lluid flow to locate anomalous regions of high temperature Ts relative to the measured value Ti at the 'same depths h thereby locating the depth and extent of injection prole throughout the permeable interval is determined from:

Q1=Qol wherein Q1 is the How rate of water into a given stratum extending between depth limits h1 and h2, Q0 is the total ow rate of injection water into the well, A1 is the integrated temperature anomaly T s-T i over the same depth limits h1 to h2, and 2A is the total of the integrated temperature anomalies for all permeable strata.

11. A method according to claim 8 in combination with the steps of introducing separate volumes of inert iluid both before and after the introduction thereinto of said reactive fluid to isolate the reactive fluid physically from said injection water within said well.

12. A method according to claim 8 wherein said reactive fluid comprises a physically stable dispersion of sdium in an inert solvent.

13. A method for determining the location of permeable strata containing a particular fluid in a plurality of strata producing several fluids and penetrated by a production bore which comprises measuring the variation in temperature of the production uid with position in said bore at least through the interval penetrating the permeable strata while continuing the normal production of the several fluids therefrom through said bore, then terminating the fluid flow within the bore, injecting simultaneously into said permeable strata a uid out of contact with fluids in said production bore and containing an agent exothermally reactive with said particular fluid present in said strata and whose presence is to be detected whereby said agent mixes and reacts with said particular iluid within said permeable strata and liberates heat therein, and remeasuring the variation in temperature of the fluid in said bore with depth within said bore opposite said permeable strata thereby detecting the depth and extent of strata containing the particular fluid from detected high temperature anomalies in the bore adjacent thereto.

14. A method for determining the depth and extent of permeable water producing strata penetrated by a production well bore in the recovery of crude petroleum and gas therefrom which comprises measuring the variation in temperature Tp of the produced fluids with depth h in said well bore at least through the interval embracing the permeable strata while continuing fluid production therefrom at the normal ilow rate, then terminating the production flow, introducing a physically isolated volume of iluid containing an agent exothermally reactive with water into said well bore, pumping the produced fluid back into said well bore for a suicient time to force the reactive fluid into said permeable strata to mix and react with any water and liberate heat therein, controlling the flow rate in said well bore to maintain the reactive fluid Volume in nonturbulent streamline ow while flowing through said well bore, then shutting in the Well, and again measuring the variation in temperature TS of the fluid in the bore with depth at least throughout the permeable interval in the absence of uid flow to locate anomalous regions of high temperature TS relative to the measured values of Tp at the same depths h which locates the depth and extent of permeable water containing strata in which heat has been liberated.

15. A method according to claim 14 wherein the water production profile throughout the permeable interval is determined from:

wherein Q1' is the flow rate of water into said well bore from a given permeable stratum between depth limits h1 and h2', Q0 is the total flow rate of water from the well, A1' is the integrated temperature anomaly Ts'-Tp over the same depth limits, and EA is the total of the integrated temperature anomalies for all permeable strata between their depth limits.

16. A method according to claim 14 in combination with the steps of introducing a volume of an inert uid ahead of the reactive fluid and another volume behind the reactive uid pumped into said well bore whereby said reactive Huid is physically isolated against premature reaction with water during transit through the bore.

17. A method according to claim 14 wherein the reactive uid comprises a physically stable dispersion of sodium in an inert solvent.

References Cited in the le of this patent UNITED STATES PATENTS 2,172,625 Schlumberger Sept. 12, 1939 2,290,075 Schlumberger July 14, 1942 2,320,643 Neufeld June 1, 1943 2,725,283 Mounce et al Nov. 29, 1955 2,740,695 Buckley et al Apr. 3, 1956 

1.A METHOD FOR LOGGING WELL BORES TO DETERMINE THE LOCATION OF WATER-CONTAINING PERMEABLE STRATA PENETRATED BY SAID WELL BORE WHICH COMPRISES MEASURING THE VARI-ATION IN TEMPERATURE OF THE FLUID WITHIN THE WELL BORE AT LEAST THROUGHOUT THE PERMEABLE STRATA INTERVAL WHILE CONTINUING NORMAL FLUID FLOW BETWEEN SAID WELL BORE AND SAID STRATA, THEN TERMINATING SAID NORMAL FLUID FLOW, THEN INJECTING INTO EACH OF SAID PERMEABLE STRATA A FLUIDD OUT OF CONTACT WITH WELL BORE FLUIDS AND CONTAINING AN AGENT EXOTHERMALLY REACTIVE WITH WATER WHEREBY SAID AGENT MIXES AND REACTS IN SAID PERMEABLE STRATA WITH SAID WATER AND LIBERATES HEAT THERIN, AND REMEASURING THE VARIATION IN TEMPERATURE OF THE FLUID WITHIN SAID WELL BORE OPPOSITE SAID PERMEABLE STRATA THEREBY DETECTING THE PRESSENCE OF WATER-CONTAINING STRATA FROM TEMPERATURE ANOMALIES CONSISTING OF REGIONS OF ABNORMALLY HIGH TEMPERATURE OPPOSITE SAID PERMEABLE STRATA. 